Whether a given page is "left" or "right" is determined by the major writing direction of the document. For example, if the first page has a major writing direction of left-to-right then it will be a :right page; if it has a major writing direction of right-to-left then it will be a :left page.

Note: This pseudo-class can be used to change only the margin, padding, border, and background properties of the page box. All other properties will be ignored, and only the page box, not the document content on the page, will be affected.